High Speed Downlink Packet Access (HSDPA) is a key technology in the Wideband Code Division Multiple Access (WCDMA) system, which can realize downlink high speed data transmission through a series of approaches, such as Adaptive Modulation and Coding (AMC), Hybrid Automatic Repeat Request (HARQ), NodeB fast scheduling and so on.
Two kinds of downlink channels are added into the WCDMA system where the HSDPA has been introduced, one is a High Speed Physical Downlink Shared Channel (HS-PDSCH) for transmitting data information, and the other is a High Speed Shared Control Channel (HS-SCCH) for transmitting control information of the HS-PDSCH. When there is no HS-PDSCH, C(256,1) is fixedly allocated to a Primary Common Control Physical Channel (PCCPCH) and C(256,0) to a Primary Common Pilot Channel (PCPICH) by a Radio Network Controller (RNC), where C(X, Y) represents a channelization code with a Spreading Factor (SF) equal to X and a code number equal to Y, and the channelization code is commonly called a code. Apart from the above two channels, other channels in the WCDMA system obtain their channelization codes by means of dynamic allocation due to the limitation of downlink code resources. After the HS-PDSCH is introduced into the WCDMA system, a cell may simultaneously have multiple HS-PDSCHs, and it is required in the WCDMA system that the channelization codes of these multiple HS-PDSCHs may be consecutive. Therefore, the RNC may generally reserve some code resources for the HS-PDSCHs. As specified in the protocols, the SFs of the channelization codes used by the HS-PDSCHs are 16, and thus, the RNC will reserve several consecutive channelization codes with the SF 16 for the HS-PDSCHs, which may not be allocated to other channels any more. According to the specifications, the maximum number of HS-PDSCHs available in each cell is 15, and these HS-PDSCHs are shared by HSDPA users in the cell.
When allocating code resources for HS-PDSCHs, various strategies can be employed by the RNC. For example, the RNC may reserve zero code resource according to practical situations, that is, reserve no code resource; or reserve code resources according to the required highest speed of a single traffic; or according to the capacity of a traffic model. Generally, the RNC determines the code resources needed by the HS-PDSCHs according to the traffic model of each cell. When traffic models and strategies for accessing bearers of a cell have been determined, the code resources reserved by the RNC for the HS-PDSCHs can primarily meet the real application demands of cell users.
However, traffic capacity of HS-PDSCHs may change with the actual demands of users. Moreover, the environment of channels may also change with the moving of users or changing of surroundings, which may lead to the changing of code resource demands of cell users. If the amount of code resources reserved for HS-PDSCHs by the RNC is small, and no appropriate adjustment is carried out according to actual demands, code resources with idle state in the system can not be used by the HS-PDSCHs, and there may be a shortage of code resources for the HS-PDSCHs, which will reduce the efficiency of code resources.